Conventional electric fans are generally provided with a speed changing device. Such a device may be a multiple-step speed selector adapted to selectively change the speed of an electric fan among various predetermined speeds, or a stepless speed changer capable of selectively changing the speed of an electric fan within certain speed range steplessly. However, there is an inconveniency in conventional speed changing devices because the device has to be operated manually when one wants to change the speed of an electric fan. Though a timing switch may be used to start or to stop an electric fan at a certain pre-set time, it is only good for starting or stopping the electric fan. It is particularly bothersome in the night when one has to get up to operate the speed changing device when the room temperature changes and one wants to increase or reduce the speed of the electric fan rather than just to start or to stop.
Therefore, it is the main object of this invention to provide a timer-controlled speed changing device for changing the speed of an electric fan in a pre-set time from one speed to another.